On Earth, biological activity

Answer choices

1. A

   Weakens8% picked this

   Life forms that have a different effect on the ratio of S-34 to S-32 from that of life forms on

   "Life did occur on Mars. The reason that this Martian meteorite only shows the pre-life ratio is because ...." .... life forms that have evolved on other planets, unlike those on Earth, don't change the ratio of S-34 to S-32.

   8%
2. B

   Weakens11% picked this

   The effects of life on the ratio of S-34 to S-32 depend on a number of climatic and environmental factors with regard

   "Life did occur on Mars. The reason that this Martian meteorite only shows the pre-life ratio is because ... " .... life forms don't necessarily change the ratio from S-34 to S-32; it's complicated; it's based on some other climate and environmental factors that are different on Earth vs. Mars. This is essentially the same as (A). We're able to argue that on Mars, life doesn't change the ratio of S-34 to S-32 because of different climate and environmental factors, so that's why even though there was life on Mars, the Martian meteorite won't show the ratio that happens on Earth when life comes on the scene.

   11%
3. C

   Correct51% picked this

   The ratio of S-34 to S-32 in the meteorite is the same as that on Mars as a whole at the time that the

   Why this is right

   One of our possible objections was that "There was life on some spots of Mars, and in those spots the ratio changed as it did on Earth. But ... this meteorite happened to come from a different spot of Mars, where life had not affected the ratio." This answer strengthens by ruling out that objection. It's saying that the ratio in the meteorite was fully representative of the ratio present on Mars when that meteorite left.

   Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.

   51%
4. D

   Weakens17% picked this

   Relatively few terrestrial mineral samples contain S-34 and S-32 in the ratio that indicates the

   "Life did occur on Mars. The reason that this Martian meteorite shows a pre-life ratio is that ... .... life doesn't usually change the isotope ratio when it comes to terrestrial minerals. This answer is weird, and I may be misunderstanding its intended thrust, but since (C) actually strengthens the argument, it's a safe bet to pick (C) and assume this somehow weakens. It seems like this answer is saying, "even in present day samples of terrestrial minerals, you can scarcely find the post-life ratio of isotopes", which suggests that terrestrial mineral samples aren't a good way to check on whether life has / hasn't shifted the ratio. A meteorite is a big chunk of rock, and rocks are terrestrial mineral deposits. So it seems like the intended force of this answer is saying, "we shouldn't really expect a meteorite to show whether or not the ratio changed on Mars, because even on Earth, where we know life has occurred and where we know life has shifted the ratio, you can barely find evidence of that shifted ratio when you check mineral samples".

   17%
5. E

   Weakens13% picked this

   The current ratio of S-34 to S-32 on Mars is different from that at the time the material

   "Life did occur on Mars. The reason that this Martian meteorite shows S-34 (the pre-life isotope on Earth) is because ...." .... this meteorite left before life started on Mars. If you went to Mars nowadays and checked out the ratio, you'd see it's the post-life ratio we see on Earth, so you'd think, "Wow, I guess Mars had life!" But since this meteorite left before life arrived, it still has that pre-life ratio that is a relic of the past.

   13%